ATAR862-3_07 Datasheet, PDF (28/112 Pages) ATMEL Corporation – Microcontroller with UHF ASK/FSK Transmitter

19.2.1
RC-oscillator 1 Fully Integrated
For timing insensitive applications, it is possible to use the fully integrated RC oscillator 1. It
operates without any external components and saves additional costs. The RC-oscillator 1 cen-
ter frequency tolerance is better than ±50% over the full temperature and voltage range. The
basic center frequency of the RC-oscillator 1 is f_O ≈ 3.8 MHz. The RC oscillator 1 is selected by
default after power-on reset.
Figure 19-2. RC-oscillator 1
RC
oscillator 1
RcOut1
Stop
RcOut1
Osc-Stop
Control
19.2.2
External Input Clock
The OSC1 or OSC2 (mask option) can be driven by an external clock source provided it meets
the specified duty cycle, rise and fall times and input levels. Additionally, the external clock stage
contains a supervisory circuit for the input clock. The supervisor function is controlled via the
OS1, OS0 bit in the SC register and the CCS bit in the CM register. If the external input clock is
missing for more than 1 ms and CCS = 0 is set in the CM register, the supervisory circuit gener-
ates a hardware reset.
Figure 19-3. External Input Clock
Ext. ^OSC1
Clock
or
Ext. ^OSC2
Clock
Ext. input clock
ExIn
ExOut
Stop
Clock monitor
RcOut1
Osc-Stop
CCS
Res
Table 19-2.
OS1
1
1
x
Supervisor Function Control Bits
OS0
CCS
1
0
1
1
0
x
Supervisor Reset Output (Res)
Enable
Disable
Disable
28 ATAR862-3
4556H–4BMCU–07/07